Anterograde and retrograde tracers are being injected into the motor, premotor, sensory and auditory cortex of the albino rat. Thes techniques are being used to identify the areas, cell types and layers which provide input into these cortical regions. Bibliographic references: J.Q. Trojanowki and S. Jacobson. A combined horseradish peroxidase-autoradiographic investigation of reciprocal connections between superior temporal gyrus and pulvinar in squirrel monkey. Brain Research 85 (1975) 347-353; S. Jacobson and J.Q. Trojanowski. Corticothalamic neurons and thalamocortical terminal fields: An investigation in rat using horseradish peroxidase and autoradiography. Brain Research 85 (1975) 385-401.